The present invention relates to an ink-jet printer capable of printing data with high printing quality. The present invention also relates to a printing method in an ink jet printer.
A non-impact recording technique is superior to other techniques due to its lower noise operation during recording, and thus is increasingly highlighted. Among other non-impact recording techniques, an ink jet recording technique has advantages that a high-speed recording can be obtained with a relatively simple structure and that plain paper can be used for a recording sheet.
Various methods have been proposed in the ink jet printing technique heretofore. An example of such methods uses ink droplets ejected by a recording head to attach onto a recording sheet and form characters or figures thereon. This method has an advantage that a fixing step is unnecessary to the record formed on plain paper as well as an advantage of a higher-speed printing, and thus various types of ink-jet printers using this method are increasingly used.
The ink-jet printers as described above are categorized roughly into three types including a continuous injection type, an on-demand type (or impulse type), and an electrostatic absorption type. The on-demand type, which ejects ink only when it is required, has an advantage of low ink consumption as well as a simple structure and is expected to be widely used.
The ink-jet printer of the conventional on-demand type, described in Patent Publication JP-B-6-45244, uses a thinning out technique for prevention of ink from blotting or running. In this ink-jet printer, the amount itself of the ejected ink in each droplet is increased when the thinning out technique is used compared to the case of an ordinary printing, thereby avoiding weakness of the record.
In the described printer, however, the thinning out technique involves a poor resolution irrespective of the increased amount of ink to thereby degrade the printing quality.
The ink-jet printer of the on-demand type, described in Patent Publication WO93/24330, achieves a high-quality printing by printing with black ink after printing with underlying color ink at a black region in the vicinity of the boundary between the black region and an adjacent colored region. More specifically, in the described printer, if there is a black region and a colored region adjacent to each other in the printing, color printing is first conducted on the black region as an underlying layer for the black ink printing, thereby preventing bleeding of ink between both the regions.
In the described printer, since the printer uses a thinning out technique, printing quality is poor due to a lower resolution. In addition, the underlying black-ink layer consumes a large amount of black ink, and increases blotting of ink or paper damage.
Patent Publications JP-A-10-81014 and -10-81012 describe ink-jet printers wherein gray-scale printing is conducted by changing the amount of ejected ink and thus changing the dot diameter of the ink dot by using a plurality of driving pulses. In these publications, a smaller ink droplet and a larger ink droplet are continuously ejected from a single ink nozzle onto the recording sheet for merging therebetween on the recording sheet.
In this technique, the larger dot diameter increases overlapping area between ink dots, which damages the recording sheet.
On the other hand, another printing technique is also known in the art wherein two different resolutions are obtained using a single waveform of the driving pulse for an ink nozzle. In this technique, the higher resolution is obtained by doubling the ordinary resolution both in the longitudinal and transverse directions while forming the dots in a zigzag line by offsetting every other dot by a half of the dot diameter to thereby preventing blank area in the record.
In this technique, the waveform of the driving pulse is common for a plurality of printing operations using different speeds and different resolutions. This involves, however, increase of dot diameters, and thus increases the overlapping areas of the printed dots, which in turn causes a damage for the recording sheet. In this technique as well as the technique described just above, the driving pulse for the piezoelectric elements is constant irrespective of difference between the types of the recording sheets, i.e., constant whether the data is printed on a plain paper or a dedicated printing sheet, by using a common dot diameter. This causes blotting of ink on the dedicated printing sheet to degrade the printing quality and paper damage of the dedicated printing sheet. This also causes smaller dot diameter of the record on a plain paper due to excessively smaller blotting, which causes weakness of the record or causes dotted lines due to incomplete printing.
Other ink-jet printers, described in Patent Publications JP-A-7-256874, -7-205454 and 4-173250, reduce bleeding of inks at the boundary between different colored regions. More specifically, the described printers, each having a recording head wherein a black ink nozzle and a plurality of color ink nozzles are arranged in a longitudinal direction, operates overlap printing at the boundary by printing with a plurality of color inks while reducing the bleeding. In this technique, printing with black ink is conducted while using a scanning technique following a printing with color ink, whereby color ink is dried to some extent before the black-ink printing to avoid the mixing or bleeding of the black ink and color ink.
In this technique, although the bleeding is reduced due to the arrangement of the color ink nozzles and the black ink nozzle, the time length for printing is increased and the printing head has a larger scale. In addition, the number of nozzles formed in the printing head is limited, which reduces resolution.
It is therefore an object of the present invention to provide an ink-jet printer capable of improving the printing quality of the ink-jet printer by reducing blotting, bleeding or mixing of inks and by reducing a paper damage.
It is another object of the present invention to provide a method used in an ink-jet printer.
The present invention provides an ink-jet printer comprising a plurality of pressure chambers each for receiving therein ink, a piezoelectric element having a plurality of separate electrodes each for responding to a driving pulse to eject the ink from a corresponding one of the pressure chambers, the piezoelectric element forming an ink dot on a recording sheet (printing media) based on the driving pulse, a mode selection section for selecting one of a plurality of printing modes, a driving signal generator for generating at least one waveform for the driving pulse based on the selected one of the printing modes, and a driving section for supplying the driving pulse to each of the separate electrodes based on the selected waveform.
In accordance with the ink-jet printer of the present invention, the amount of ejected ink can be selected for each ink dot by selecting the waveform of the driving pulse based on the selected printing mode such as in accordance with the type of the recording sheet, resolution or printing speed. Thus, bleeding or mixing of ink can be reduced as well as the paper damage, whereby an excellent printing quality can be obtained.
The term xe2x80x9cink-jet printerxe2x80x9d as used herein means an ordinary ink-jet printer used for a computer, for example, as well as an ink-jet recording device such as a facsimile or copying machine, so long as the recording device uses an ink-jet printing technique therein.
The present invention also provides a method for printing an image on a recording sheet (printing media) comprising the steps of specifying a printing mode out of a plurality of printing modes, selecting at least one waveform out of a plurality of waveforms based on the specified printing mode, and driving a piezoelectric element based on the selected waveform.
In accordance with the method of the present invention, since the driving pulse can be controlled based on printing mode such as in accordance with the type of the recording sheet, resolution or printing speed, deficiencies such as blotting, bleeding or mixing of ink can be reduced on either a plain paper or a dedicated printing sheet.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.